Hunter syndrome is a lethal lysosomal storage disorder caused by the deficiency of iduronate-2-sulfatase (IDS) and characterized by severe skeletal and neurological symptoms.
Hunter syndrome, {mucopolysaccharidosis (MPS) type II}, results from a defect in the gene encoding the iduronate-2-sulfatase (IDS) (EC 3.1.6.13), which hydrolyzes 2-sulfate groups from nonreducing terminal iduronide moieties of glycosaminoglycan (GAG) molecules (Neufeld E F, J Biol Chem 264: 10927-10930, 1989; Hopwood J J and Morris C P, Mol Biol Med 7: 381-404 1990; Whitley C B et al., Hum Mutat 2: 235-237, 1993). The defect is generally due to point mutations or deletions in the 24 Kb-long gene, mapped on Xq28.2 (Le Guern E et al., Genomitcs 1990; 7: 358-362). The disorder clinically manifests as coarse facial features, skeletal deformities (dysostosis multiplex) with short stature and related physical disability, joint contractures, hepatosplenomegaly, and cardiopulmonary deterioration. In severe cases, children experience progressive mental retardation and die before the age of 15. Patients with relatively mild forms have normal intellect, but typically succumb to cardiac and respiratory disease in early adulthood (Young I D and Harper P S, Hum Genet 60: 391-392, 1982; Young I D and Harper P S., Dev Med Child Neurol 25: 481-489, 1983).
At present, there is no fundamental effective method for treating for Hunter syndrome. Bone marrow transplantation (BMT) has been suggested as one possible therapeutic method.
Previous attempts at systemic therapy were based upon in vitro observations showing the restoration of normal GAG catabolism when IDS-deficient fibroblasts are cocultured with cells having normal enzyme activity (Fratantoni J C et al, Science 162: 570-572, 1968). Similar results were obtained from coculturing with normal lymphocytes or macrophages (Olsen I, et al., Nature 291: 244-247, 1981; Olsen I et al., J Cell Sci 55: 211-231, 1982; Dean M F et al., J Cell Sci 79: 137-149, 1985; Di Natale P et al., Biochim Biophys Acta 1138: 143-148, 1992). Such studies provided important insights into the fact that most lysosomal enzymes can be transferred to other cells not only by mannose-6-phosphate (M6P) receptor-mediated endocytosis (Neufeld E F., Annu Rev Biochem 60: 257-280, 1991), but also by direct cell-to-cell contact (Olsen I et al., Nature 291: 244-247, 1981) Some clinical trials involving BMT have demonstrated therapeutic responses in relevant tissues (Warkentin P I et al., Birth Defects Orig Artic Ser 22: 31-391986; Resnick J M et al., Bone Marrow Transplant 10: 273-280, 1992), suggesting its clinical potential for lysosomal storage diseases.
However, the application of BMT has been limited by the lack of histocompatible donors, its complications, graft-versus-host disease, and the morbidity and mortality rate of the procedure. Recently, affected blood cells were metabolically corrected with retroviral vectors expressing normal IDS enzyme in vitro (Braun S E et al., Proc Natl Acad Sci USA 90: 11830-11834, 1993; Braun S E et al., Hum Gene Ther 7: 283-290, 1996). A phase I clinical trial was carried out in one patient using a retoviral vector (Whitley C B et al., Hum Gene Ther 7: 537-549, 1996). Accordingly, gene therapy involving the transfer of normal IDS gene to a patient's autologous bone marrow stem cells has been suggested as an alternative method to the conventional BMT. The key to the success of this gene transfer technology is to develop a safe and efficient gene delivery vehicle.
The present inventors previously reported the construction of retroviral vectors with improved safety, gene expression and versatility (U.S. Pat. No. 6,451,595; Kim S H et al., J Virol 72: 994-1004, 1998; Yu S S, et al., Gene Ther 7: 797-804, 2000). These new vectors, unlike previously developed ones, contain no viral coding sequences but still manage to produce high viral titer and drive high levels of gene expression in transduced cells. Because these vectors do not have any overlapping sequences with packaging genomes, the possibility of homologous recombination is virtually nil and thus the vectors are expected to be safer than the others currently available.
The present inventors have constructed three types of retroviral vectors that can be used for gene therapy of Hunter syndrome, MT-IDS, MIN-IDS, MIM-IDS, using a minimum sized MLV-based retroviral vector, MT, as a backbone. Among the vectors examined, retroviral vector MT-IDS lacking a selectable marker has been found to give a highest viral titer and leads to a highest level of expression of IDS in transduced cells, and, therefore, it may be advantageously used for gene therapy of Hunter syndrome.